This invention relates to a method and apparatus for detecting the end of a performance in a record player by discriminating variations in the pitch of the record groove.
With a record player, reproduction is carried out by moving a pick-up cartridge needle along the spiral groove of a record placed on a rotating turntable. Most modern record players employ automatic tone arm return systems. In one of such systems the tone arm return is initiated by detecting the arrival of the pick-up at a position which lies at a predetermined distance from the center of the turntable. In another system the increased pitch of the lead-out groove of a record is utilized. That is, increments in the differentiated output of a signal which varies in correspondence to the radial movement of the pick-up are detected to thereby discriminate the end of a performance and return the tone arm.
The former system is disadvantageous in that when a record whose lead-out groove is relatively close to the outer circumference is used, the automatic return function does not work. In contrast, when a record whose lead-out groove is relatively close to the center is used, the tone arm will be returned before the performance is ended.
In the latter system if the spindle hole in the center of the record is not exactly coincident with the center of the recording groove, the tone arm oscillates one cycle during each revolution of the record due to the eccentricity of the hole. As a result, the output signal corresponding to the position of the pick-up also varies or oscillates. Accordingly, if an increment of the radial pick-up movement speed is detected by differentiating this signal, an output increment Q.sub.1 (FIG. 1) obtained when the signal varies in a positive direction due to the eccentricity of the record is greater than the average increment Q.sub.2, and such an artificially high differentiation output leads to a premature and erroneous return operation.